In the poultry industry, particularly the production of chicks, methods are known for automatic egg candling using the transparency of the egg at the end of the incubation period in order to differentiate two categories of eggs: full eggs that are opaque to light comprising not only fertilized eggs containing an entirely-developed embryo, alive or dead, but also contaminated or rotten eggs, and eggs that are permeable to light comprising unfertilized eggs, called clear eggs, but also the underdeveloped eggs containing a prematurely dead embryo. These methods consist in emitting a luminous flux towards an egg to candle and then analyze the luminous flux that has passed through the egg in order to determine its fertilized or unfertilized state, based on the luminous flux rate absorbed by the egg. With that end, the system usually comprises a device for emitting a luminous flux, a receiver for receiving the luminous flux that has passed through the egg and a processor for electronically processing the luminous flux received via the receiving means. The electronic processor is thus able to roughly differentiate the eggs according to the luminous flux rate absorbed by the egg. At the end of the incubation period, the fertilized egg containing a normally-developed living embryo is opaque. However, so are the eggs containing an embryo which died late or contaminated and rotten eggs. The latter are hence not easy to differentiate from normally-developed eggs. As for the eggs that are permeable to light at the end of the incubation period, they either correspond to infertile eggs or to eggs containing a prematurely dead embryo, without it being possible to distinguish them in a reliable manner.
This candling method by transparency thus does not make it possible to differentiate with certainty the live eggs from the dead eggs at the end of the incubation period. Moreover, it is not adapted to be used at a more premature stage of the development cycle of the egg, for example between the 3rd and 17th day of the incubation cycle of the hen's egg. It does not make it possible to know with certainty the fertilized or unfertilized state of the egg at the beginning of the cycle due to the insignificant size of the embryo. It does not provide either more precise data on the living or dead state of the embryo at an intermediate stage of the incubation cycle and/or on its development state (normal development or not of the embryo at this same intermediate stage of the incubation cycle). Furthermore, it is not adapted either to determine an inverted or uninverted state of the egg based on the position of its air cell. Finally, it gives no data on the integrity of the egg shell, namely the presence or not of cracks on the shell.
Alternatively, a candling carried out manually using a source of white light does not make it possible either to compensate for the aforementioned drawbacks due to the poor visibility of the inner structures of the egg.